Sooner or later we all need to take a screenshot. Here are the keyboard commands that let you do it fast in Mac OS X Lion. Your screenshots will be saved to your desktop as a .PNG file.
1. Take a screenshot of the entire screen: Shift+Command+3.
2. Take screenshot of a specific window: Shift+Command+4 then hit Space.
3. Take screenshot of a particular area of the screen: Shift+Command+4 then click and drag around the area you want to capture.
If you prefer to have your screenshot saved to the clipboard instead of as a file on your desktop just hold the Control key while using the commands above.
How to Take Screenshots in Mac OS X | Hack College